Display devices such as organic EL panels have been used for various electronic equipments such as displays of cellular phones, car audio systems, or the like. In recent years, further enlargement of the organic EL panel has been sought.
This organic EL panel may have a constitution where an organic layer is sandwiched between two electrodes which are formed on a substrate so as to face each other. By impressing the electric field between the electrodes, the organic layer emits light.
In order to lead out the luminescence of the organic layer externally, at least one of the electrodes should be designed as a transparent or semitransparent electrode. However, since the transparent or semitransparent electrode possessed a relatively large electrical resistance in general, the organic EL panel is used to cause unevenness of brightness in the luminescence due to a certain voltage drop.
In order to solve this problem, an electrically conductive material, that acts as an auxiliary electrode to lower resistance, has been formed in accordance with the vapor deposition method or other known methods. (This electrically conductive material is called “bus line”.).
It becomes easy to flow to the electrode in the current by forming the bus line that consists of the electrically conductive material, and the degression of voltage can be prevented.
Patterning of the bus line has been done by using the photolithograph method etc., to make the bus line to narrow width comparatively because the bus line should not disturb the luminescence of organic EL panel.
Since a certain influence against the organic layer in the photolithograph process is considered, in general, an electrode and the bus line are formed on the substrate in advance of forming the organic layer on the substrate.
Recently, in order to prevent the voltage drop, improvements in material of the bus line and in the width and thickness of the bus line has been further developed so as to lower the resistance of the bus line (Patent literatures 1 and 2).    [Patent literature 1]    Japanese Patent Laid-Open 2002-277855    [Patent literature 2]    Japanese Patent Laid-Open 2003-297584